Additive manufacturing systems are used to build 3D parts from digital representations of the 3D parts (e.g., AMF and STL format files) using one or more additive manufacturing techniques. Examples of commercially available additive manufacturing techniques include extrusion-based techniques, ink jetting, selective laser sintering, powder/binder jetting, electron-beam melting, direct metal laser melting (DMLM), and stereolithographic processes. For each of these techniques, the digital representation of the 3D part is initially sliced into multiple horizontal (X-Y) layers. For each sliced layer, a tool path is then generated, which provides instructions for the particular additive manufacturing system to form the given layer.
Current powder bed DMLM machines are fraught with limitations, especially those preventing large-size scalable systems, the limitations including but not limited to speed, powder volume, trapped powder, and thermal stresses. Speed limitations include recoating and laser scan times that are too slow. Current processes are essentially 1-D (point melting) repeated in X-Y space and then repeated in Z space. Typical layers require 300 seconds of laser time followed by 10 seconds of recoat time. Powder volume limitations exist because every nook and cranny of the build cube must be filled with powder requiring large volumes of powder charges which must be dealt with during and after build. For large area builds, this powder charge could be thousands of pounds. Also, trapped powder limitations occur because closed volumes are impossible to build as the powder cannot be evacuated. The current requirement to evacuate powder also limits design freedom. And, current DMLM machines impose large thermal stresses on parts resulting from rapid build material solidification thereby creating geometrical distortions and sometimes cracking in the parent material. In addition, the entire platform must be stress relieved prior to cut-off which is difficult for large parts due to the heavy loads and size limitations of commonly accessible furnaces.
In two-dimensional (2D) printing, electrophotography (i.e., xerography) is a popular technology for creating 2D images on planar substrates, such as printing paper. Electrophotography systems include a conductive support drum coated with a photoconductive material layer, where latent electrostatic images are formed by charging and then image-wise exposing the photoconductive layer by an optical source. The latent electrostatic images are then moved to a developing station where toner is applied to charged areas of the photoconductive insulator to form visible images. The formed toner images are then transferred to substrates (e.g., printing paper) and affixed to the substrates with heat or pressure.
However, a need exists for improved printing techniques for 3D printing, particularly with metal build materials.